The present invention generally relates to endoprosthesis devices and to a method for making same. More particularly, the invention relates to a generally tubular endoprosthesis that includes a non-woven structure. The non-woven structure may include one or more layers of stiff strand material wound in a generally helical shape. The strand forming one layer may be bonded to the strand forming another layer at their mutual points of contact thereby facilitating the circumferential adjustability and flexibility of the device. Fixing the non-woven structure at the bonding points further allows the structure to be cut to various lengths and angles without the risk of fraying or unraveling. The non-woven structure allows the endoprosthesis to be deformed as desired in a permanent, non-uniform manner for irregularly shaped vascular system applications. The method used to make the present invention allows the architecture of the non-woven structure to be varied according to the application to which the device is put.
Blood vessels or other hollow organs may suffer from a variety of failings and disabilities such as abnormal widening (aneurysm), abnormal localized contraction or lesion growth (stenosis or occlusion), or abnormal narrowing (stricture). One surgical and medical technique employed to correct defective blood vessels or other hollow organs utilizes the insertion of a vascular endoprosthesis, commonly referred to as a "stent", in the blood vessel or other hollow organs. An endoprosthesis device of this type is typically placed or implanted by a mechanical transluminal procedure. Where the blood vessel or other hollow organs are abnormally widened, the stent is inserted to provide inner support to the blood vessel wall and to prevent further dilation and possible actual rupture. Where the endoprosthesis is used to treat a stenotic condition, the vessel must first be widened or dilated. Typically, this is done in association with a dilation element such as an angioplasty balloon. The dilation element is used to open the narrowing. Because stenotic lesions typically have a high fibrocollagenous content, the opened blood vessel or other hollow organs may begin to close upon removal of the dilation element. To prevent, or, at least, slow the post-dilation narrowing of the inner blood vessel wall tissue (that is, restenosis), a stent may be inserted contemporaneously. The insertion of the stent avoids the use of traditional surgical solutions to vascular problems. These traditional solutions carry with them inherent complications such as vessel wall dissection, subintimal flap formation, rupture, pseudoaneurysm formation, spasm, and late vessel narrowing (stenosis).
To accomplish the application objectives, a stent must be flexible, yet mechanically durable. A stent must be flexible so that it can be maneuvered within the blood vessel or other hollow organs without causing damage to the vessel. A stent must be flexible also so that it may be bent to the shape of the vessel in which it is positioned. Flexibility is necessary further because the stent may be located in an area which undergoes considerable movement or flexing.
The durability requirement for a stent arises largely from the methods conventionally utilized to deploy stents. For example, in one deployment method, a stent is compressed circumferentially so that it be may fitted within a tubular body, such as a catheter. The tubular body and stent are inserted percutaneously and moved to the desired vascular location, where the stent is released. The stent may also be deployed by compressing it to a diameter small enough to fit snugly around a collapsed angioplasty balloon. This assembly is then introduced into the blood vessel and moved to the affected area, at which location the balloon is expanded. The stenotic lesion is dilated and, upon the deflation of the balloon, the now expanded stent remains to prevent restenosis. In this deployment method, the stent must be sufficiently flexible in order to expand along with the balloon, yet be mechanically durable so the stent does not collapse during expansion. The stent must be also mechanically durable so the stent structure can support the dilated tissue during its possible recoil and withstand the movement or flexing which takes places in certain vascular locations. A stent which cannot withstand mechanical stress will fracture thereby causing the traumatization of the surrounding blood vessel.
Conventionally, stents may be made from various materials. If the stent is formed from wire-like elements, the wire is generally made from metal or a metal alloy. One type of stent, such as the type taught in Alfidi et al. U.S. Pat. No. 3,868,956, utilizes a specific type of metal alloy with "memory function", that is, the ability to recover its initial configuration upon heating. By using such an alloy, a stent, in a non-compressed state, may be inserted into a blood vessel, heated, and thereby expanded to the original desired shape.
A variety of stent structures are conventionally known. For example, one type of expandable graft is made from woven stainless steel wire whose cross points are soldered with silver. A woven prosthesis similar to this type is taught in Wallsten U.S. Pat. No. 4,655,771. Another type of stent utilizes a spring-like wire structure. By tightly coiling the spring, a stent with a relatively small profile is produced which may be inserted through a blood vessel. By releasing the spring, the stent uncoils at the place of implantation. Illustrative of this type of coiled spring stent or endoprosthesis is Mass, et al. U.S. Pat. No. 4,553,545. A similar use of a compressed spring-like expandable element is taught in Wiktor U.S. Pat. No. 4,649,922. A multi-helix or braided stent which is also expandable is taught in Palmaz U.S. Pat. No. 4,733,665. Additionally, a closed pattern characterizes the structure of the percutaneous endovascular stent formed of stainless steel wire taught in Gianturco U.S. Pat. No. 4,580,568.
The present invention advantageously retains most of the desirable features of the various conventional stents or endoprosthesis, while avoiding many of their various deficiencies. In summary, the generally tubular endoprosthesis of this invention includes a generally slender, tubular body member formed from one or more layers of strand material. The strand material from which the body member is formed is not interwoven but is fabricated in a manner similar to that detailed in U.S. Pat. No. 4,475,972 to Wong, which is incorporated by reference hereinto. In the present invention, the strand material providing the non-woven structure is made preferably from any suitable non-elastomeric material. The strand may be drawn onto a mandrel to form two or more components which are continuously helical in shape. In an embodiment of the present invention, the strand may be drawn onto the mandrel to form layers. The strand orientation of adjacent layers may be the same or different and are typically generally opposite to each other. Each successive layer may be bonded together at the points at which the strand material overlaps in order to provide a mechanically durable, yet highly flexible structure whose architecture may be adjusted according to the needs of each particular application. Regardless whether the stent is single-layered or multi-layered, each layer may be approximately equal in thickness to the diameter of the strand material.
It is a general object of the present invention to provide an improved generally tubular endoprosthesis.
Another object of the present invention is to provide an improved endoprosthesis or stent having a tubular body formed from at least one or more non-woven layers.
Another object of the present invention is to provide an improved endoprosthesis or stent whose non-woven structure allows the device to be permanently shaped to conform to the irregularities of the vascular system.
Another object of the present invention is to provide an improved endoprosthesis or stent having a non-woven structure which permits the device to be cut into various lengths and angles without collapsing, fraying or unraveling.
Another object of the present invention is to provide an improved endoprosthesis or stent having a non-woven structure which is bound so that the endoprosthesis or stent may be flexible and accept compression or expansion and retain full structural integrity.
Another object of the present invention is to provide an improved endoprosthesis or stent which is of a uniform and low profile structure that insures consistently predictable performance and use within areas of limited dimensions.
Another object of the present invention is to provide an improved endoprosthesis or stent which is readily expandable by an expanding member such as the balloon of a catheter device.
These and other objects, features, and advantages of this invention will be clearly understood through consideration of the following detailed description.